The invention relates to analog-to-digital converter compensation systems and methods.
Analog-to-digital (AID) converters generate three types of errors during operation: (i) random, wideband noise, (ii) spurious tone components that are not correlated to, nor harmonically related to, an input tone, and (iii) spurious tone components that are correlated to and harmonically related to an input tone (systematic error). Compensation algorithms are not presently available for wideband noise or spurious, non-correlated components.
However, tones due to systematic error are typically tones which result from recurring, repeatable errors in the output, and can thus be compensated. Repeatable systematic errors are highly correlated with two measurable values: the analog-to-digital index and the trajectory of the waveform at the time the analog-to-digital index was generated.
Conventional compensation techniques typically include training sequences such as: collecting error measurements from a large variety of training data, classifying each error sample collected according to its analog-to-digital index, and keeping a separate running total of error values and sample counts for analog-to-digital indices. After training and during operation (compensation), for each incoming analog-to-digital sample to be compensated, the address is found in the compensation table from the index, and the average error value at the address is subtracted this from the input value to get the compensated output.
Frequency domain algorithms to generate the training data are described in U.S. application Ser. No. 11/017,458, filed 20 Dec. 2004 and entitled “Analog-to-Digital Converter Compensating Apparatus and Associated Methods.” Briefly, the general idea is to take a discrete Fourier transform (DFT), such as a fast Fourier transform (FFT) for example, of the input signal, then zero out the bins corresponding to random noise or other uncorrectable spurious components, and then finally inverse transform the modified spectrum back into the time domain. In this embodiment, to avoid energy leakage between the bins, the training frequencies are selected to fall on DFT bin frequencies (by locking together the analog-to-digital sampling clock and training signal generator).
It would be desirable to have an analog-to-digital converter compensation system and method which do not have the design constraints of conventional techniques.